Ok.. you have a domain. that's good.
there's alot to do and alot of questions to be answered for email to work.
1. if you have a website and its hosted by a third party, do they provide email as well?
2. If not... are you going to use the SBS 2003 exchange server for email?
3. do you have internet at the office and if so... do you have a firewall device?
4. where is your domain's Name service being hosted?
If you are planning to do it all at your site... you need.
1. Internet connection to a router.
2. A Firewall device like sonicwall with TCP/IP port 25 and 80 passed through to your email and webserver.
3. Your ISP providing a name service for your domain
4. a SBS 2003 server with Exchange and IIS configured for web services, DNS configured, WINS configured, DHCP configured, file and printer sharing
5. Windows workstations configured with DHCP for automatic IP addressing, Outlook pointing towards your SBS2003 server for email and a default route to your firewall to provide internet browsing.
If you are planning a third party to host the website and email, you only need the internet router with all incoming ports blocked and all normall outgoing ports enabled. Your SBS2003 server would provide DHCP, DNS, WINS and file/printer sharing. You set up your workstations's outlook to point to the third party's email server. You could still use the exchange server on the SBS2003 box and have it eturn the email from the third party server to yours.
This of course is over simplified. there's alot involved and it takes some planning and time to implement. Any more.. and I'll have to charge you though! :-)